This invention concerns an apparatus for cutting helically wound metal tubing, and relates more especially to a cutting apparatus that can be installed within a machine for producing helically wound metal tubing to enable lengths of tubing to be severed as the tubing issues from the machine.
It is known to sever lengths of helically wound tubing as it issues from a machine by cutting means that is adapted to travel longitudinally with the moving tubing, in order to cut the tubing in a transverse plane. Such devices are known, for example, from U.S. Pat. Nos. 957,966, 3,132,616 and 4,706,481.
In order to cut metal tubing of relatively light gauge metal sheet, for example of the kind formed from a helically wound strip, there can be used either a rotary slitting saw, or a pair of cooperating slitting wheels operating from the inside and outside of the pipe, one of the wheels being forced through the wall of the pipe to overlap the other so that the wall of the pipe is cut in a shearing action. Such a mechanism has now become commonplace in the domestic can-opener. A mechanism of this kind adapted for the cutting of the wall of a metal tube is known from U.S. Pat. No. 4,054,069 and comprises cutting rollers, one of which is mounted for rotation on a boom arranged to extend within the hollow pipe, and the other of which is mounted externally of the pipe and guided for movement in a direction normal to the wall of the pipe in order to penetrate the latter and overlap the internal cutting roller.
Although such cooperating slitting wheels are normally driven to rotate when cutting, the application of such a cutting mechanism to a machine for the helical winding of metal tubing involves the difficulty that the association of the cutting wheels with a carriage arranged to travel relatively to the forming head of the machine cannot easily be achieved whilst maintaining a drive transmission to the shafts upon which the cutting wheels are mounted.
Thus, for example, as described in U.S. Pat. No. 4,706,481 it is proposed to dispense with any mechanism for driving the cutting wheels, and to leave them to rotate idly in contact with the metal tubing that rotates as it issues from the machine. Whilst such an arrangement has proved effective for cutting metal tubing having a relatively low wall thickness, it does have the disadvantage that additional stresses are placed upon the main drive of the machine that is required to advance the metal strip through the helical forming head, since the driving rollers contacting the metal strip are now required not only to drive the strip around the helical path defined by the forming head, but also to overcome the resistance to rotation of the tube due to the cutting mechanism.